FYI: DW_FORM_ref_addr -vs- DWARF 3

FYI: DW_FORM_ref_addr -vs- DWARF 3

[Tom Tromey]

I'm checking this in.  I will probably push it into 7.1 as well; let me
know what you think of this.

DWARF 3 changed DW_FORM_ref_addr to use an offset-sized value instead of
an address-sized value.  GDB does not cope with this, which can cause
crashes.  For a real-life example:

    https://bugzilla.redhat.com/show_bug.cgi?id=552619

I found this in the archives, after writing my patch:

    http://sourceware.org/ml/gdb-patches/2006-06/msg00286.html

I guess it was never reviewed?  I dunno.  Anyway, I prefer my patch.

Built and regression tested on x86-64 (compile farm).
I also verified it before- and after- on the test program I have.

Tom

2010-03-04  Tom Tromey  <tromey@redhat.com>

	* dwarf2read.c (skip_one_die) <DW_FORM_ref_addr>: Use offset size
	in DWARF 3 and later.
	(read_attribute_value) <DW_FORM_ref_addr>: Likewise.

diff --git a/gdb/dwarf2read.c b/gdb/dwarf2read.c
index a05c946..b2558f0 100644
--- a/gdb/dwarf2read.c
+++ b/gdb/dwarf2read.c
@@ -2881,8 +2881,15 @@ skip_one_die (gdb_byte *buffer, gdb_byte *info_ptr,
     skip_attribute:
       switch (form)
 	{
-	case DW_FORM_addr:
 	case DW_FORM_ref_addr:
+	  /* In DWARF 2, DW_FORM_ref_addr is address sized; in DWARF 3
+	     and later it is offset sized.  */
+	  if (cu->header.version == 2)
+	    info_ptr += cu->header.addr_size;
+	  else
+	    info_ptr += cu->header.offset_size;
+	  break;
+	case DW_FORM_addr:
 	  info_ptr += cu->header.addr_size;
 	  break;
 	case DW_FORM_data1:
@@ -7016,8 +7023,14 @@ read_attribute_value (struct attribute *attr, unsigned form,
   attr->form = form;
   switch (form)
     {
-    case DW_FORM_addr:
     case DW_FORM_ref_addr:
+      if (cu->header.version == 2)
+	DW_ADDR (attr) = read_address (abfd, info_ptr, cu, &bytes_read);
+      else
+	DW_ADDR (attr) = read_offset (abfd, info_ptr, &cu->header, &bytes_read);
+      info_ptr += bytes_read;
+      break;
+    case DW_FORM_addr:
       DW_ADDR (attr) = read_address (abfd, info_ptr, cu, &bytes_read);
       info_ptr += bytes_read;
       break;

Re: FYI: DW_FORM_ref_addr -vs- DWARF 3

[Joel Brobecker]

Hi Tom,

> 2010-03-04  Tom Tromey  <tromey@redhat.com>
> 
> 	* dwarf2read.c (skip_one_die) <DW_FORM_ref_addr>: Use offset size
> 	in DWARF 3 and later.
> 	(read_attribute_value) <DW_FORM_ref_addr>: Likewise.

This patch looks fine to me for head and branch. I don't know which
version I prefer, between Jim's and yours, but yours is smaller :). 

-- 
Joel

Re: FYI: DW_FORM_ref_addr -vs- DWARF 3

[Tom Tromey]

>>>>> "Joel" == Joel Brobecker <brobecker@adacore.com> writes:

Joel> Hi Tom,
>> 2010-03-04  Tom Tromey  <tromey@redhat.com>
>> 
>> * dwarf2read.c (skip_one_die) <DW_FORM_ref_addr>: Use offset size
>> in DWARF 3 and later.
>> (read_attribute_value) <DW_FORM_ref_addr>: Likewise.

Joel> This patch looks fine to me for head and branch. I don't know which
Joel> version I prefer, between Jim's and yours, but yours is smaller :). 

:)  Thanks, I checked this in to the 7.1 branch as well.

Tom